An iron (II) porphyrin complex contained in hemoglobin or myoglobin reversibly adsorbs and desorbs oxygen molecules. Many studies for producing synthetic complexes which have oxygen adsorption and desorption functions similar to those of natural porphyrin iron (II) complexes have been reported: J. P. Collman, Accounts of Chemical Research, 10, 265(1977), and F. Basolo, B. M. Hoffman and J. A. Ibers, ibid, 8, 384(1975). As a porphyrin iron (II) complex from which a stable oxygen complex is produced at room temperature, an iron (II) 5,10,15,20-tetra(.alpha., .alpha., .alpha., .alpha.-o-pivalamidephenyl)porphyrin complex is reported (J. P. Collman et al., The Journal of the American Chemical Society, vol. 97, p.1427(1975)).
However, the complex is unable to produce a stable oxygen complex because it is easily oxidized by oxygen in the presence of a small amount of water. Accordingly, an iron (II) porphyrin complex which produces a stable oxygen complex at room temperature has been continuously researched. The inventors of the present invention have found that oxygen is reversibly adsorbed and desorbed in an aqueous solution by inclusion of these iron porphyrin complexes in lipid molecular membranes. (Publication number of examined patent application: 59-25767/1984 and Publication number of laid-open patent application: 59-101490/1984).